1. Field of the Invention
The invention generally relates to data communications in a millimeter wave network, and more particularly, to the re-design of a header of a Control Physical layer (CPHY) for transmitting data.
2. Description of the Related Art
Millimeter wave (mmWave) technology allows for a new era in multigiga bits per second (bps) wireless communications for consumer electronics because of the huge available bandwidth worldwide. For example, 7 GHz (from 57-64 GHz) of unlicensed spectrum is available in the United State and Source Korea and 9 GHz of unlicensed spectrum is available in Europe.
The standards in 60 GHz wireless networks, such as the IEEE 802.11aj standard, IEEE 802.11ad, and Wireless Gigabit Alliance (WiGig), have been developed or are being developed by different industry consortiums and international standard organizations. The WiGig and IEEE 802.11ad standards are two promising standards with a majority of support from industry. It is very likely that the upcoming 802.11aj standard adopts the physical layer specification of the IEEEE 802.11ad standard.
In mmWave WPAN and IEEE 802.11ad, control PHY (CPHY) and data PHY (DPHY) are defined. In the Table 1, CPHY and Lowest rate DPHY transmit at very low data rates and are used for discovery mode. DPHY transmits at high data rates and is used for data communications. Generally, CPHY is operated in an omni-directional mode or quasi-omni directional mode and DPHY is operated in a directional mode. Therefore, DPHY requires higher signal-to-noise-ratio (SNR) than CPHY. For current mmWave WPAN based on the WiGig and IEEE 802.11ad standard, the minimum SNR requirement of DPHY is 12 dB (e.g. −1−(−13)=12 dB) higher than SNR required by CPHY, i.e. if the SNR difference of DPHY and CPHY is not higher than 12 dB, the DPHY may not work. The true SNR difference is limited by the size of the antenna array at the Space-Time Antenna (STA) and is defined by the condition: (True SNR difference)<10*log10 (number of antenna elements). Therefore, the STA must be equipped with an antenna array of more than 16 elements.
TABLE 1DATARequiredTYPEMCSRATESNRCPHYDBPSK, ~½ code, Spreading 27 Mbps−13 dB32Lowest DPHYBPSK, ~½ code, Repetition 32385 Mbps −1 dB
However, antenna arrays with a large number of antenna elements are not suitable for mobile devices due to size factor. Therefore, coverage problems may occur. For example, for a mobile device equipped with 4 antenna elements, SNR of the DPHY is just 6 dB (10 log104˜6<12) higher than the SNR of CPHY. Therefore, CPHY works fine but DPHY does not work. Namely, the mobile device can be associated with access point (AP) or personal basic service set central point (PBSS central point, PCP), but can't transmit/receive any data.